The heart is the center of a person's circulatory system. It includes an electro-mechanical system performing two major pumping functions. The heart includes four chambers: right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV). The left portions of the heart, including LA and LV, draw oxygenated blood from the lungs and pump it to the organs of a body to provide the organs with their metabolic needs for oxygen. The right portions of the heart, including RA and RV, draw deoxygenated blood from the organs of the body and pump it to the lungs where the blood gets oxygenated. The efficiency of the pumping functions, indicative whether the heart is normal and healthy, is indicated by measures of hemodynamic performance, such as parameters related to intracardiac blood pressures and cardiac output.
In a normal heart, the sinoatrial node, the heart's natural pacemaker, generates electrical impulses, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite the myocardial tissues of these regions. Coordinated delays in the propagations of the action potentials in a normal electrical conduction system cause the various portions of the heart to contract in synchrony to result in efficient pumping functions indicated by a normal hemodynamic performance. A blocked or otherwise abnormal electrical conduction and/or deteriorated myocardial tissue cause dysynchronous contraction of the heart, resulting in poor hemodynamic performance, including a diminished blood supply to the organs of the body. The condition where the heart fails to pump enough blood to meet the body's metabolic needs is known as heart failure.
The adult myocardium is incapable of repairing itself after an injury. Such an injury may result from, for example, myocardial infarction (MI), which is the necrosis of portions of the myocardial tissue resulted from cardiac ischemia, a condition in which the myocardium is deprived of adequate oxygen and metabolite removal due to an interruption in blood supply. The adult heart lacks a substantial population of precursor, stem cells, or regenerative cells. Therefore, after the injury, the heart lacks the ability to effectively regenerate cardiomyocytes to replace the injured cells of the myocardium. Each injured area eventually becomes a fibrous scar that is non-conductive and non-contractile. Consequently, the overall contractility of the myocardium is weakened, resulting in decreased cardiac output. As a physiological compensatory mechanism that acts to increase the cardiac output, the LV diastolic filling pressure increases as the pulmonary and venous blood volume increases. This increases the LV preload, including the stress on the LV wall before the LV contracts to eject blood. The increase of the LV preload leads to progressive change of the LV shape and size, a process referred to as remodeling. Remodeling is initiated in response to a redistribution of cardiac stress and strain caused by the impairment of contractile function in the injured tissue as well as in nearby and/or interspersed viable myocardial tissue with lessened contractility due to the infarct. The remodeling starts with expansion of the region of the injured tissue and progresses to a chronic, global expansion in the size and change in the shape of the entire LV. Although the process is initiated by the compensatory mechanism that increases cardiac output, the remodeling ultimately leads to further deterioration and dysfunction of the myocardium. Consequently, the myocardial injury, such as resulted from MI, results in impaired hemodynamic performance and a significantly increased risk of developing heart failure.
Thus, there is a need to improve the properties of implanted medical devices.